1. Field of the Invention
The present invention relates to a differential case for a vehicle and a differential devise for a vehicle including the differential case, and more particularly relates to the differential case for the vehicle and the differential devise for the vehicle having a pinion gear supporting portion supporting slidably a pinion gear which is a shaft-less type.
2. Description of the Prior Art
It is well known for a prior differential device for a vehicle to provide a pair of shaft-less pinion gears as disclosed in a published patent document; Tokkai 2006-46642.
This differential device for the vehicle comprises a differential case rotated by torque from an engine, a pair of pinion gears, a pair of side gears engaging in mesh with the pair of pinion gears in a state that an axis of the pinion gears is perpendicular to that of side gears, a pair of thrust washer receiving thrust force from the pair of side gears.
The pair of pinion gears has a gear peripheral portion as a supported portion over all around periphery and a gear engaging portion engaging in mesh with the pair of side gears and the pair of pinion gears are disposed in the differential case on an axis perpendicular to a rotational axis of the differential case.
The differential case is equipped with a pair of wheel shaft inserted holes. The differential case is also equipped with a pinion gear inserted hole having first pinion gear supporting surface to support slidably, that is rotatably, peripheral surfaces of a pair of pinion gears. On a peripheral edge of an inner opening of the pinion gear inserted hole is formed a second pinion gear supporting surface supporting slidably a part of the gear engaging portion of the pinion gear.
The pair of side gears is constructed with an annular bevel gear having a large diameter than that of the pinion gears and is installed on a rotational axis of the differential case. An inside surface of the pair of side gears is connected with right and left tire shafts in a spline engagement.
A pair of thrust washers is installed between back surfaces of the pair of side gears and an annular inner opening edged of a pair of the wheel shaft inserted holes. It can be adjusted a degree of intermeshing engagement of the pair of side gears with the pair of pinion gears by the thrust washers.
Based on the above-mentioned construction of the prior art, when torque from an engine is input into the differential case through a driving pinion and a ring gear, the differential case is rotated around the rotational axis. At the rotation of the differential case, the rotational force is transmitted to the pair of pinion gears and the pair of side gears through the pair of pinion gears. Therefore, the torque is distributed and transmitted differentially to right and left tire shafts through the drive pinion, the ring gear, the differential case, the pair of pinion gears and the pair of side gears according to a running condition of the vehicle since the pair of side gears engages with right and left tire shafts in the spline engagement.
In running of the vehicle, the pinion gears slide on the first pinion gear supporting surface and the second pinion gear supporting surface upon the rotation of the pinion gears, frictional resistance is occurred between the first pinion gear supporting surface and the pinion gears and also between the second pinion gear supporting surface and the pinion gears to restrict the differential rotation of the side gears.
And also in this time, another thrust force of an intermeshing surface of the pinion gears with the side gears, therefore, this thrust force acts the pair of side gears to be moved to separated directions each other. In this result, there occurs another frictional resistance between the thrust washers and the thrust washer receiving portions to restrict the differential rotation of the side gears also.
However, in the differential device for the vehicle of the published patent document of Tokkai 2006-46642 as the prior art, since an extending portion is formed on the annular inner opening edge of the pinion gear inserted holes and a free edge of the extending portion is not fixed, a bending stiffness of the extending portion is poor by receiving the load from the side gears through the pinion gears. As a result, it is easy to deform the extending portion to change and move an intermeshing position between the pinion gears and the side gears so that it restricts stable differential restriction force upon occurrence of excessive torque.